This invention relates to printing machines and particularly to a numbering machine of the kind used for printing repeatedly incremented numerical or alpha numerical codes on a train of documents.
One intended use of the invention is in a multistage machine, usually called web machine, employed for the printing of documents, e.g., bank notes. In such a machine a paper web, on which a train of documents is printed, is continuously transported at comparatively high speed through a multiplicity of printing and treatment stages, including a numbering station. Such a numbering station usually comprises a numbering cylinder which carries at least one set of numbering barrels, the barrels in each set being at spaced locations around its periphery. The printing cylinder co-operates with an impression roll to form a printing nip. Usually the numbering station is downstream from various printing stages which print, in one or more columns, a multiplicity of documents.
However the invention is also applicable where the documents are presented separately but in rapid succession.
It is usual for the numbering barrels on each printing cylinder to be incremented by a suitable modulus automatically between successive discrete angular positions so as to produce (though not necessarily from a single printing cylinder) a continuous series of numbers on the pre-printed documents when the machine is running normally. In such a machine as has been described, it would be desirable to cease overprinting by means of the numbering cylinder if a "spoil" document were detected. It will be understood that where overprinting is to be performed on documents which are printed as part of a continuous web, and the web contains random "spoil" documents (otherwise called misprints) it is desirable to inhibit the printing of, for example, a number in the series on the "spoil" document so that, after the documents have been individually separated from the web and the spoil documents have been removed, the remaining "good" documents bear respective numbers or alpha numeric codes in an unbroken sequence.
Numbering machines of the kind with which the present invention is concerned can be adjusted so that the incrementing of the numbering barrels can be inhibited for long runs but hitherto have not been adapted for the selective inhibition of incrementing such that randomly occurring "spoil" documents are not overprinted, i.e., they are omitted from the numbering sequence.
It is known from European Patent Application No. 85303863.6 (published Dec. 27, 1985 as EP-A2-0165734) to provide a spoil detector which can provide, in real time, scanning of documents on a continuously moving web and a control signal which denotes a "spoil" document. The present invention may be used in conjunction with such a detector.